1. Field of the invention
The present invention relates to a joining loop structure of an industrial multilayer fabric for preventing exposure of lower side warps from the surface of the fabric, in particular, a joining structure of an airlaid multilayer fabric.
2. Description of the Related Art
As industrial fabrics, many fabrics, for example, paper manufacturing fabrics such as a paper making fabric and a paper making canvas, nonwoven cloth manufacturing fabrics, sludge dewatering fabrics, building material manufacturing belts, and conveyor belts have heretofore been known. At present, these industrial fabrics are processed as endless ones and used after attached to individual machines such as a paper making machine and a dehydrator.
Examples of a method of obtaining an endless industrial fabric by processing include a method of connecting both ends of an industrial fabric by weaving, a method of engaging loops formed on both ends by using the warp of the industrial fabric itself with each other and inserting a joining core wire through a common hole of these loops, a method of engaging spiral loops installed at both ends of the industrial fabric with each other and inserting a core wire through these loops, and a method called clipper lacing, in which metal hooks attached to both ends of the fabric are engaged with each other and then, a core wire is inserted through the resulting hooks. These known methods are employed, depending on their intended use.
Particularly, in the method of engaging loops formed at both ends of an industrial fabric with each other, thereby obtaining an endless fabric, an endless fabric or a disjoined fabric can be made freely by inserting or extracting the joining core wire. If an endless fabric or a disjoined fabric can be made freely, it is possible to extend the disjoined fabric between rollers of a device and then make the fabric endless while having it between rollers. Thus, using this method enables very easy and efficient attachment of the fabric to the device.
For example, the device can be operated after an old used industrial fabric attached to the device is formed to have ends and one end of a new industrial fabric to be attached is joined to one end of the old fabric. The industrial fabric is moved and extended between the rollers of the device and after confirmation that the fabric is moved around and entirely extended, the old industrial fabric is removed and thus, the new industrial fabric can be attached in an endless manner.
On the other hand, in the method of joining both ends of an industrial fabric by weaving, by which an endless or disjoined industrial fabric cannot be formed freely, a so-called cantilever system should be employed. In this system, the rollers of the device are supported on one side, supports and other obstacles are removed from the other side, and the industrial fabric is inserted and extended in a width direction from one side of the device. However, using the cantilever system for joining has such a disadvantage as an increase in the manufacture cost of the machine, because the machine itself requires a special structure for attaching or removing the fabric. In addition, disadvantages such as increase in the size of the device and requirement of a wide space for installing the device have also been pointed out. Moreover, when a very heavy or long industrial fabric is used, the system is unsuited because it is difficult to insert the fabric.
The above-described cantilever system is therefore not employed now in most cases excluding paper making fabrics used in the paper making section of a paper making machine in which surface smoothness is regarded as very significant. As the method of forming an endless fabric, a method of forming a spiral loop or a metal hook at the end portion which method permits formation of the fabric in a disjoined form again is employed.
In the above-mentioned method, however, a spiral wire or metal hook made of a material utterly different, in structure or materials, from a yarn constituting an industrial fabric should be attached. Even if a loop is formed, the loop formation portion differs from a normal portion and the loop protrudes from the end portion. Thus, the structure of a joining portion is completely different from that of the normal portion.
As the two-layer fabric for nonwoven cloth described in Japanese Patent Application No. 2011-87484, industrial double-layer fabrics obtained by binding an upper side fabric and a lower side fabric with a binding yarn are known. Such a fabric is used in the manufacturing method of a nonwoven cloth so that different yarns are used for the upper side fabric and the lower side fabric, respectively. Described specifically, in the double-layer fabric for nonwoven cloth described in Japanese Patent Application No. 2011-87484, the upper side fabric is made of a fluorine-based resin to prevent fouling and the lower side fabric is made of a general yarn such as polyethylene terephthalate (PET) to satisfy requirements in physical properties such as rigidity.
When a loop is formed as a joining structure of both ends of such an industrial fabric, a difference in the structure between the loop formation portion and the normal portion becomes a problem. In the case of Japanese Patent Application No. 2011-87484, since the loop formation portion should be made of a yarn such as PET stronger than a fluorine-based resin, the loop is formed with the lower side warp. In the loop formation portion, however, the lower side warp made of PET or the like is exposed from the surface, which deteriorates the effect and advantage of the upper side fabric made of a fluorine-based resin to prevent fouling.
As the joining portion described in Japanese Patent No. 3938817, on the other hand, a joining loop structure in which a loop formation portion is positively hided with an upper side weft is known. An object of the invention described in Japanese Patent No. 3938817 which is related to a joining loop, however, is to form the loop formation portion and the normal portion without causing a significant difference between them. No consideration is given to prevent exposure of the lower side fabric from the surface so that this invention has the disadvantage that the lower side warp constituting the loop is exposed from the surface.